Process of reducing the sensitiveness of silver compounds and products



UNITED STATES PATENT- OFFICE;

NATHAN SULZBERGER, 0F N'EW YORK, N. Y.

rnocnss or annucme THE SENSITIVENESS or SILVER COMPOUNDS AND rnonuc'rs.

No Drawing. Application filed April 26, 1915, Serial No. 24,148. Renewed September 7, 1920. Serial.

- Specification of Letters Patent.

Patented Oct. 19, 1920.

To all whom it may coacem:

Be it known that I, NATHAN SULZBERGER,

- born in New York city, and a citizen of the United States,

resident of New York city, in the county and State of New York, have invented new and useful Im rovements in Processes of Reducing the ensitiveness of Silver Compounds and Products, of which the following is a specification.

The means generally employed in photography of produc ing pictures permanent to the action of light, consist in dissolving out of the developed plate (film, etc.) or out of the print (copy), as in the case of gaslight copying paper andlthe like, by the aid of sodium thiosulfate the compounds articularly of silver, 'as the chlorid an romid, which are still sensitive to the action of light, after development or printing of the visible picture. This method requires not only great lengths of time, which are necessary in order to effect the complete solution of the sensitive silver salts, still remaining in the material, and also in particular, to

wash out the last traces of the thiosulfate,

which must be accomplished so as to produce lasting pictures, directions often speak of from 12 hours but also large amounts of water, making the process inconvenient and in many cases impossible, as particularly, when traveling and in certain climates. I w

I have found, that these objections, as well as also others, described below and ac- ;ompanied with the use of sodium thiosulate,

- by my method of photography. The same consists in reducing to a larger or smaller extent the sensitiveness toward light of photo-actinic substances, principally the silver compounds, as the silver chlorid and silver bromid, still remaining in the photographic material after development (as in the case of plates, diapositives, films, gaslight papers, etc.) or printing of the picture (as in the case of daylight photo-copying papers, etc.). As will be seen in examples described'below, the process requires only a few minutes time and little water. In fact in instances water has been, forwashing purposes, entirely dispensed with, it having been possible to produce simply using the solutions and instead of ictures by washing out) drying off the one solution, before placing the material in the other.

are more or less completely obviated Since the process does not require the use of sodium thiosulfate, the same is necessarily also free from the disadvantages connected with the use of this salt, which, as is known, often acts also upon the silver contents of the picture, not only dissolving small amounts of such silver, particularly in the presence of air, but particles of the silver picture are also removed in .a mechanical way, when the thiosulfate acts as a solvent for the silver, chlorid and bromid. For

these reasons particularly, the unfixed picture (negative) generally will show more,

ever I wish to particularly emphasize that the below described method and quantities employed can be variously modified without leav ng the scope of my process and invention.

The paper was developed by means of,-

rnetol-hydroquinone, the developing agent simply washed out by holding for about .half a minute under running water, then placed in a solution of potassium ferrocyanid (K,,FeCy- +ag.), containing about 15% of the salt. The print can be exposed to the action of light when being placed in this solution for, say, half a minute. 'After a few minutes the picture was taken out of the solution and dried, after having been again washed for about half a minute in running water. In some cases it may be preferable to use between the developing agent and the ferrocyanid, a bath containing a suitable substance to destroy the action of the developer, as for instance, sodium bisulfite (sulfurous acid, etc.). In either case a picture results, which can be exposed to daylight, Without undergoing the change,

which such picture will rapidly undergo,

out of the picture the silver salts, still remaining in the same and soluble in sodium thiosulfate, this can readily be done. By treating such pictures with various compounds the tone and color of the same can easily be modified. Thus, pictures which have been desensitized with a ferrocyanid, will take on a brownish coloration when treated, for example, with cupric sulfate, while treatment with a ferric compound will produce a bluish coloration. Rosanilin hydrochlorid produces a pinkish or reddish tone.

As a further example I describe below the preparation of a negative of es ecial value in connection with X-ray Roentgen-) photography.

fter exposure the plate was developed and, after washing for half a minute in running water, was placed in a bath of sodium bisulfite for a minute or two, again washed as above, and placed in a solution containing less than 1% of palladiumammonium-protochlorid for a few minutes. After washing as above, the plate was dried, which process can be quickly accomplished, since the palladium compounds have a marked hardening effect upon the plate. The efle'ct' in fact of the palladium compounds in this respect is so great that such plates have even been placed in boiling water without undergoing apparently any change. Since, therefore such plates may be dried at a higher temperature than can be done when developed and fixed in the ordinary way, an additional advantage is gained (saving of time, etc. when using this method. The plates, a ter treatment with the alladium compounds, may be exposed to light, the picture remainin clearly visible, especially when holdin t e same before a brilliant source of lig t. I have exposed such plates for many weeks to light and was able to clearly view the details in the negative. Although the same still contain silver compounds soluble in thiosulfate, the surgeon can clearly and carefully study the result of his exposure, and even make prints-( ositives), if so desired. Accordingto t 's process, it is-possible to study the negative within about a minute after its development. The same will in many cases also show more details (even in cases where the plate was under-exposed) than after treatment with the thiosulfate. The hardening effect of the palladium compounds also protects the (plates, so that the same do not suffer so mu from handling. If desirable to dissolve out the silver compounds still soluble in sodium thiosulfate, this can readily be done at convenient time.

Since no developing agent is required, as is the case when working with gas-light paper, the. process is still simpler, when copying a negative on day-light paper containing silver chlorid. It is only necessary after printing and washing, picture, for instance, in a solution containing about 15% of'potassium ferrocyanid for to place the a couple of minutes. After washing for a minute the picture is desensitized and can be safely exposed to daylight. The same can be toned, if desired. A treatment with thiosulfate is unnecessary.

All such modifications of the process, which will suggest themselves to those skilled in the art of photography and chemistry shall be considered as coming under the scope of this invention. Also therefore other compounds and mixtures (as for instance with formaldehyde, alum, acids, as

for instance, phosphoric, etc.) may be e'mployed which are of a nature adapted to reduce the sensitiveness of the photo-actinic material, for example, by neutralizing any remaining developer. Instead of potassium ferrocyanid, other soluble ferrocyanids, or derivatives or mixtures thereof, may be used, as well as mixtures in which the soluble ferrocyanids are produced previous to or during the course of the desensitizing process; as well as other compounds and sub stances having a similar action.

The term photo-prints used in the following claims includes reproductions (positive as well as negative) by the action of light with or without the use of a developing agent in a photo-sensitive material contaming a silver compound.

I claim:

1.' The process of reducing the sensitive- -ness toward light of light sensitive silver light of which has been reduced, and out of which silver compounds may be dissolved by treatment with sodium thiosulfate.

5. Photo-prints, containing light sensitive silver com ounds, the sensitiveness of which toward lig t has been reduced by means of reagents reacting with such silver compounds, said photoprints still containin amounts, if only traces, of such employed reagent.

6. Pictures on gaslight paper, containing silver c'omplounds, the sensltiveness of which toward lig t has been reduced by means of potassium ferrocyanid.

7. Photo-prints containing light sensitive sllver compounds, the sensitiveness toward light of which has been reduced by means of-soluble ferrocyanid and still containing amounts, if only traces, of such ferrocyanid and" silver compounds soluble in sodium thiosulfate. p

8. Toned photo-prints containing silver compounds, the sensitiveness toward light of which has been reduced by' means of potassium ferrocyanid, and amounts, if only-traces, ofsubstances alter ing the tone of such pictures.

9. The process of reducing the sensitiveness toward light of light sensitive silver compounds employed in gas-light papers containing which comprises subjecting such compounds to the action of a solution containing a soluble ferrocyanid.

10. The process of reducing the sensitiveness toward light of light sensitive silver compounds employed in gas-light papers which comprises subjecting such compounds to the action of a solution containing potassium ferrocyanid.

NATHAN SULZBERGEB.

vVitnesses:

WOLDEMAR HAUPT,

FRIEDR. ICHRISTOBHERS. 

